Australian carrier Telstra said in a support document that it has since deleted that RCS support would be available starting with an iOS update coming in December. If that timeframe remains accurate, iPhone users on Telstra would likely be able to use RCS in the Messages app starting with iOS 27.3.
RCS support features and carrier list
RCS offers several advantages over traditional SMS for messaging with Android users, including end-to-end encryption, read receipts, typing indicators, in-line replies and more. Apple maintains a list of supported carriers.
